Expansible tube valves of the type shown in U.S. Pat. Nos. 3,272,470 and 3,306,569 have proven very effective, particularly in pressure regulation service. Such valves include a slotted core with a barrier across it between inlet and outlet flow slots. An expansible tube is stretched to seal around the barrier, normally to isolate the inlet and outlet slots. The core and expansible tube are carried within a housing, with a jacket fluid pressure normally asserted around and against the outer surface of the expansible tube to constrict it against the outer sealing surface of the barrier. Commonly, the jacket is pressurized from the upstream line whereby the pressure around the expansible tube and that asserted against the interior through the upstream slots are in balance. Consequently, sealing is effected largely through the stretch of the expansible tube around the barrier sealing surface. This requires a highly finished sealing surface as well as appreciable stretch, to insure against leak paths. Then, when the jacket pressure is reduced and is overcome by the upstream pressure the expansible tube tends to snap open with a sudden outward stretch which leads to over-action and less than completely stable operation.